In driving a motor vehicle having a manual transmission, excessive wear on the clutch is caused by lack of synchronization of engine speed with drive speed when shifting gears. In order to economize, and to simplify the instrument panel in an automobile, a tachometer dial is often eliminated from all but high performance automobiles.
Prior patents have not provided a simple, clear, combined speedometer and tachometer. Powell, U.S. Pat. No. 3,807,350 describes a speedometer dial having a plurality of windows through which selected speed and gear indicia carried on a rotatable rear plate are seen. Only a small range of indicia of each category are visible through the windows. Helgeby, U.S. Pat. No. 2,702,520, shows a combined tachometer-speedometer in which a single pointer, bearing an attached flag for each gear number, indicates engine revolutions and vehicle speed on several scales marked on the front of a single dial. Thus, knowing the gear in which the vehicle is being operated, the vehicle speed can be read from the dial. There is no indication as to the engine speed required in a different gear for the same vehicle speed.